title: Effect of reactive oxygen species on K+ contractures in the rat diaphragm.
abstract: Reactive oxygen species (ROS) are postulated to alter low-frequency contractility of the unfatigued and fatigued diaphragm. It has been proposed that ROS affect contractility through changes in membrane excitability and excitation-contraction coupling. If this hypothesis is true, then ROS should alter depolarization-dependent K+ contractures. Xanthine oxidase (0.01 U/ml) + hypoxanthine (1 mM) were used as a source of superoxide anion eliciting oxidative stress on diaphragm fiber bundles in vitro. Diaphragm fiber bundles from 4-mo-old Fischer 344 rats were extracted and immediately placed in Krebs solution bubbled with 95% O2-5% CO2. After 10 min of equilibration, a K+ contracture (Pre; 135 mM KCl) was induced. Fiber bundles were assigned to the following treatment groups: normal Krebs-Ringer (KR; Con) and the xanthine oxidase system (XO) in KR solution. After 15 min of treatment exposure, a second (Post) K+ contracture was elicited. Mean time-to-peak tension for contractures was significantly decreased in Post vs. Pre (16.0 +/- 0.7 vs. 19.8 +/- 1.0 s) with XO; no change was noted with Con. Furthermore, peak contracture tension was significantly higher (31.5%) in the XO group Post compared with Pre; again, no significant change was found with KR. The relaxation phase was also altered with XO but not with KR. Additional experiments were conducted with application of 1 mM hypoxanthine, with results similar to the Con group. We conclude that the application of ROS altered the dynamics of K+ contractures in the rat diaphragm, indicating changes in voltage-dependent excitation-contraction coupling.
authors.affiliation: Respiratory Muscle Laboratory, Eloise Beard Smith Human Performance Laboratories, Department of Health and Kinesiology, Texas A&M University, College Station, Texas 77843-4243, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Lawler
authors.forename: Z
authors.initials: Z
authors.lastname: Hu
authors.forename: W S
authors.initials: WS
authors.lastname: Barnes
mesh_terms: D000818:Animals; D003964:Diaphragm / Q000187:drug effects / Q000201:enzymology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D017382:Reactive Oxygen Species / Q000502:physiology*; D014969:Xanthine Oxidase / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D014969:Xanthine Oxidase; D011188:Potassium